1. Field of the Invention
The present invention relates to a hologram observation sheet for having a predetermined image or message reproduced in the vicinity of the point light source to be observed at the time of observing a point light source through a hologram, to be bonded onto for example a window pane, so as to be used such as for an advertisement medium, a decoration member or various kinds of filters. Furthermore, the present invention relates to a blinding device for having a predetermined image or message reproduced in the vicinity of the point light source to be observed at the time of observing the source through a predetermined position, using in particular a phase type Fourier transform hologram in a binding device which is not showing a transmitted background sharply, and a method for producing a blinding device.
2. Description of the Related Art
Recently, various articles such as glasses or paper fans, using a transmission type hologram have been proposed (for example, Japanese Patent Application Laid Open (JP-A) Nos. 2004-126535 and 2004-77548). However, according to any of them, a transmission type hologram and another member can hardly be formed integrally so that they are produced by preliminarily producing only a transmission type hologram portion, and interposing the transmission type hologram between other members. Therefore, a problem is involved in that the production process is complicated, and it can hardly be used for various applications.
On the other hand, conventionally, as a blinding device, there is a frosted glass, a pattern glass, a blind, or a roll screen as an example.
Moreover, the specification of the U.S. Pat. No. 5,546,198 proposes hologram eyeglasses. The hologram eyeglasses have the configuration as shown in the perspective view of FIG. 13A. That is, two transmission type holograms 32, 33 are set in the frames for eyes of an eyeglass frame 31. In viewing a scene including light sources of small areas 34, 35, 36, 37 as shown in FIG. 13B, while wearing the eyeglasses using the transmission type holograms 32, 33, it appears, for example as shown in FIG. 13C. Alternatively, the patterns “NOEL” 38, 39, 40, 41 appear overlapped in the vicinity of the light sources 34, 35, 36, 37. That is, it is observed as a scene with the light sources of a small area in the real scene of FIG. 13B replaced respectively by the pattern “NOEL” 38, 39, 40, 41 selected in advance. As the transmission type holograms 32, 33 having such characteristics, a Fourier transform hologram of the above-mentioned pattern “NOEL” provided as a computer generated hologram (Fraunhofer hologram) is used.
FIG. 14A is a flow chart showing a production method for such a transmission type hologram (JP-A No. 10-153943). FIG. 14B is a schematic diagram for explaining the flow chart. In the step 101, an original image 51 is produced. Then, in the step 102, a Fourier transform image 52 of the original image is produced using a computer. Then, in the step 103, a multi-valued Fourier transform image 53 is produced by multi-valuing the Fourier transform image 52 to more than the binary system. Then, in the step 104, simulation of a reproduced image is carried out. The simulation is for examining whether or not the process in each of the above-mentioned steps has been carried out appropriately by obtaining a reproduced image 54 through applying an inverse Fourier transform to the multi-valued Fourier transform image 53. Then, in the step 105, the obtained multi-valued Fourier transform image is arranged to a desired range. For example, by arranging four binarized Fourier transform images 53, a computer generated hologram 55 is obtained. In reality, the image 53 of the minimum unit is arranged by for example 10 each in the vertical and lateral directions. Then, in the step 106, an original master for copying for the computer generated hologram 55 with such an arrangement is produced using for example a semiconductor process (photolithography and etching). Then, in the step 107, the concavo-convex relief pattern of the original master for copying is copied on for example an ultraviolet ray curing resin to obtain transmission type holograms 32, 33.
Moreover, as a production method for a computer generated hologram (CGH corresponding to the above-mentioned multi-valued Fourier transform image 53) for example, the Gerchberg-Saxton iterative calculating method as disclosed in pp. 36-39 of the 22nd winter seminar text “hologram and diffraction type optical element—from basic theory to industrial application—” organized by the Optical Society of Japan (Japan Society of Applied Physics) is known. The method will be explained briefly with reference to FIGS. 15 to 17.
FIG. 15 is a diagram schematically showing a computer generated hologram 60 and an image area 70 reproduced thereby. The computer generated hologram 60, as a Fourier transform hologram, comprises an assembly of minute cells 61 having a vertical direction (y axis direction) size δy and a lateral direction (x axis direction) size δx, arranged like a lattice, with each cell 61 provided with only the phase information. The cells 61 are disposed by 2m pieces in the x axis direction and 2n pieces in the y axis direction.
On the other hand, an image area 70 provided sufficiently remotely from the computer generated hologram 60 is an assembly of cells 71 disposed by 2m pieces in the x axis direction and 2n pieces in the y axis direction, corresponding to the computer generated hologram 60. Each cell 71 has a vertical direction (y axis direction) size Δy and a lateral direction (x axis direction) size Δx, and the entire image area 70 has an x axis direction length of Lx and a y axis direction length of Ly.
The x axis direction length Lx and the y axis direction length Ly of the image area 70 each relates to the x axis direction size δx and the y axis direction size δy of the cell 61 of the computer generated hologram 60. They can be represented by the diffraction angle from the computer generated hologram 60 (since the image area 70 is provided at a position sufficiently remote from the computer generated hologram 60, Lx, Ly can be represented by an angle preferably). Lx corresponds to the range between the ± primary diffraction light of a diffraction lattice having a spatial frequency 1/(2δx), and Ly corresponds to the range between the ± primary diffraction light of a diffraction lattice having a spatial frequency 1/(2δy). This corresponds to the fact that the maximum spatial frequency recorded in the computer generated hologram 60 is 1/(2δx) in the x axis direction, and 1/(2δy) in the y axis direction.
With such a positional arrangement, in the case a parallel light 80 of a predetermined wavelength is incident from the front surface of the computer generated hologram 60, a diffraction light 81 is generated on the rear surface side of the computer generated hologram 60 so that the pattern recorded in the computer generated hologram 60 is reproduced in the remote image area 70.
Here, in order to facilitate understanding, the amplitude distribution (pixel value) of the original image in the reproduced image surface 70 is represented as AIMG (x, y), the phase distribution of the original image in the reproduced image surface 70 as φIMG (x, y), the amplitude distribution of the hologram surface 60 as AHOLO (u, v) and the phase distribution in the hologram surface as φHOLO (u, v). As shown in FIG. 16, in the step 201, the pixel value of the original image to be recorded is provided as the AIMG (x, y) in the reproduced image surface 70 for initializing the phase distribution of the original image to a random value, and in the step 202, the Fourier transform is applied to the initialized value. In the step 203, a constraints for setting the amplitude distribution AHOLO (u, v) in the hologram surface 60 obtained by the Fourier transform to 1, and the phase distribution φHOLO (u, v) to a predetermined multi-value (quantinization) is provided. After providing such constraints, in the step 204, the Fourier inverse transform is applied to the amplitude distribution AHOLO (u, v) and the phase distribution φHOLO with the constraints applied. In the step 205, in the case the amplitude distribution AIMG (x, y) in there produced image surface 70 obtained by the Fourier inverse transform is substantially equal to the pixel value of the original image by the convergent criterion, the phase distribution φHOLO (u, v) processed to be a multi-value (quantinization) in the step 203 provides the phase distribution to be supplied to the cells 61 of the computer generated hologram 60. In the case the amplitude distribution AIMG (x, y) obtained by the Fourier inverse transform is not judged equal to the pixel value of the original image in the convergent criterion of the step 205, the constraints of providing the pixel value of the original image instead of the amplitude distribution AIMG (x, y) obtained by the Fourier inverse transform and leaving the phase distribution φIMG (x, y) obtained by the Fourier inverse transform as it is, is provided in the step 206. After providing the constraints, a loop of the steps 202→203→204→205→206 is repeated until the condition of the step 205 is satisfied (converged) so as to obtain a final computer generated hologram 60 desired.
Without carrying out the multi-value process for the phase distribution φHOLO (u, v) in the step 203, a predetermined multi-value process may be carried out after satisfying the condition of the step 205.
From the multi-valued phase distribution φHOLO (u, v) accordingly obtained, the depth distribution of the real hologram is calculated. The phase distribution φHOLO (u, v) is converted to the depth D (u, v) of the computer generated hologram 60 based on the following formula (1):D(u,v)=λφHOLO(u,v)/{2π(n1−n0)}  (1).Here, λ is the used central wavelength, and n1, n0 are the refractive indexes of the two materials comprising the transmission type hologram. In the case of the transmission type, as shown in the cross-sectional view of FIG. 17, the computer generated hologram 60 can be obtained by forming a relief pattern 83 of the depth D (u, v) obtained by the above-mentioned formula (1). The case of FIG. 17 is an example with the φHOLO (u, v) multi-valued in the four stages of 0, π/2, π, 3π/2. The above-mentioned coordinates (u, v) in the hologram surface 60 are for distinguishing from the coordinates (x, y) in the reproduced image surface 70 so that as to the coordinate axis directions, the u axis direction corresponds to the x axis direction, and v axis direction corresponds to the y axis direction, respectively.
Moreover, in addition thereto, as the prior art, pp. 33-36 of “Butsurigaku Sensho 22 Holography” written by Junpei TSUJIUCHI (published by SHOKABO PUBLISHING CO., Ltd. (Nov. 5, 1997) can also be presented.
However, the above-mentioned conventional blinding devices proposed are simply for a single purpose of preventing the transmitted background from being seen sharply without providing the optical design property so that most of them have ordinary and dull appearances. Moreover, the optical information transmission is not possible in the conventional blinding devices.
Moreover, as to those for transforming a point light source to a desired pattern using a hologram for a blinding device, due to the extreme difficulty for realizing a large size, at present, those of a large size are not produced, and the production method therefor has not yet been established.